In the field of this invention it is known that many parts of a wireless communications receiver often require an estimation of noise variance and/or SIR. This is needed for purposes of power control, threshold determination for various algorithms, quantisation of soft-decision information for channel decoding purposes to name but a few.
For BPSK (Binary Phase Shift Key) and QPSK (Quadrature Phase Shift Key) modulation the conventional method for estimating the SIR at the output of a detector relies on estimating output noise variance using the following equality known (for example) from the publication by Papoulis and Pillai, entitled ‘Probability, Random Variables and Stochastic Processes’, 3rd Ed. 1991,{circumflex over (σ)}z2=E(|{circumflex over (d)}n(k)|2)−E(|{circumflex over (d)}n(k)|)2 
where {circumflex over (σ)}z2 represents variance, E represents mean value and {circumflex over (d)}n(k) the detector output.
This yields the following result:
      SIR          (      k      )        =                              P                      (            k            )                          -                              σ            ^                    z          2                                      σ          ^                z        2              =                            E          (                                                                d                ^                            n                              (                k                )                                                          )                2                                          E            (                                                                          d                  ^                                n                                  (                  k                  )                                                                    )                    2                -                              E            (                                                                          d                  ^                                n                                  (                  k                  )                                                                    )                    2                    
where SIR represents the SIR of the kth sequence at the detector output, and P(k) represents the average power of the kth sequence at the detector output.
However, this approach has the disadvantage(s) that the accuracy of this method at low SIR is poor since it suffers from a bias term. An analysis of the bias term and a correction method has been suggested in UK Patent Application GB 0128475.1 (UK Publication No. GB 2 382 748 A and titled “Signal to noise plus interference ration (SNIR) estimation with correction factor” to applicant IPWireless) filed on Nov. 28, 2001. However, the suggested correction method requires a look-up table to correct for the aforementioned problem, and the estimation variance is also increased when correcting the bias.
A need therefore exists for a method and arrangement for noise variance and SIR estimation wherein the abovementioned disadvantage(s) may be alleviated.